A significant problem in the chemical and petroleum industry is the high energy costs associated with the separation of mixtures by distillation, and in particular with the separation of fluid streams having three or more components. This has become especially true in recent years with the substantial rise in energy costs. As a result, there is a need to develop distillation systems that provide for adequate separation of the components, at a lower energy cost. Some fully thermally coupled distillation systems provide some energy cost savings; however, due to control difficulties these distillation systems have generally not been commercially used. Thus there is a need for energy efficient methods to separate fluid streams. The present invention answers this need by providing a method and apparatus, which separates a mixture of benzene, toluene, and alkyl benzene, wherein a relatively high portion of toluene is present in the feed, while reducing the overall heat duty required by the distillation systems.
A conventional method for the separation of benzene, toluene, and alkyl benzene is disclosed in U.S. Pat. No. 4,246,073 where the initial feed stream contains a molar ratio of benzene-toluene-alkyl benzene at about 3:2:1.